A variety of oligomerization catalysts, both homogeneous and heterogeneous, have been utilized to oligomerize ethylene into olefinic products or alkenes of higher molecular weight. Linear Alpha Olefins (LAO) or Normal Alpha Olefins (NAO) in a C4-C28 hydrocarbon range are commercially manufactured by using various ethylene oligomerization processes including the Shell Oil Company SHOP process (using a molecular active Ni catalyst) or Ineos process (Ethyl Corporation) or Gulf process (ChevronPhillips Company) or Sabic Linde α-Sablin process or IFP-Axens AlphaSelect process, where alky aluminum catalysts (typically Ziegler Natta type systems) are used to produce even number carbon alpha olefins with a statistical bell curve shape of carbon number distribution (Schulz-Flory distribution).
Ethylene dimerization and trimerization processes are also known. For example, the IFP-Axens Alphabutol Process and Dimersol E technologies employ titanium-containing catalysts for dimerization. The ethylene trimerization process to produce 1-hexene using a chrome-containing catalyst was commercialized by the ChevronPhillips Company.
Ethylene feeds for these processes are produced by an on-purpose ethylene producing plant where pure ethylene with 99.99%+ purity is isolated using very expensive, state-of-the art distillation columns. Ethylene dimerization, trimerization, and oligomerization processes typically use only pure ethylene for their feeds since the dimerization, trimerization, and oligomerization catalysts are extremely susceptible to poisoning by impurities. Even a small amount of poisons such as sulfur, nitrogen containing compounds, oxygenates, dienes, and trace metals can deactivate the catalysts.
The petrochemical and petroleum industry produces many hydrocarbon streams containing ethylene. However, the separation of pure ethylene from these process streams and/or separation of impurities for catalytic operations are often not undertaken nor economical (due to the added processing unit operations) and the streams are commonly used as lower value fuels to generate steam.
Conventional catalysts such as zeolite or mineral acid cannot oligomerize ethylene to make jet and diesel range hydrocarbon with acceptable conversion and selectivity. Use of an ionic liquid catalyst for alkylation of ethylene with isoparaffins was described in, for example, U.S. Pat. No. 7,432,408 and US Patent Application No. 2011/0319693 where ethylene was reacted with isopentane or isobutane to make alkylate gasoline products, predominantly C7 or C6 hydrocarbon.
There is a need for a process that can be applied to a mixed hydrocarbon stream containing ethylene to oligomerize ethylene into a high value hydrocarbon product using ionic liquid catalysts to obtain jet and diesel fuel and satisfy the increasing market demand for hydrocarbons in the jet and diesel fuel range. Furthermore, there is a need for an ethylene oligomerization process in which high ethylene conversion and good diesel selectivity are obtained from a feed stream containing low-purity ethylene.